Hot melt adhesives of the above mentioned type are known per se. For example, reactive hot melt adhesives based on epoxy resins are used in the car industry. These known: epoxy adhesives are, however, not very flexible in the cured state. The glueings obtained with them admittedly display a high tensile strength, but easily crack as a result of peeling under traverse stress. It is a known problem that adhesives with which high tensile shearing strengths can be achieved often provide only a low level of T-peel strength.
In the car industry, a frequent procedure when glueing sheet metal is firstly to apply the adhesive in a warm, but not yet cured state. Upon cooling, the adhesive sets and, accompanied by the formation of adequate handling strength, provides a provisional bond. The sheets thus bonded to each other are treated in washing, parkerizing and dip-coating baths. Only then is the adhesive cured in an oven. Therefore a need exists for hot melt adhesives which already display an adequate wash-out resistance prior to curing.
It is known from DE-A-32 02 300 to add polyols to epoxy resins to increase their flexibility. Epoxy resins modified with alcohols are described in DE-A-34 09 188. Known from EP-A-01 30 741 are polyoxypropylene amines or amino-terminated polypropylene glycols (ATPPG) and their use as curing agents for epoxy resins.
In DE-C-26 59 928 and DE-C-26 59 989 aqueous dispersions are described which contain epoxy resins and dicyanodiamide as curing agents. The aqueous dispersions are used as coating agent. However, high tensile shearing and T-peel strengths are not relevant with coating agents.
It is known from DE-A-38 27 626 to improve the flexibility of reactive hot melt adhesives based on epoxy resin by adding a linear polyoxypropylene with amino end-groups during the preparation of the resin component. In this way an improvement of the properties is achieved, particularly of the flexibility and of the peel strength. However, the properties at low temperatures down to -40.degree. C. in particular are still not satisfactory. For example, in the winter it is not rare for motor vehicles to be exposed to temperatures far below 0.degree. C.